I'm trying to figure out something I don't know.
I'm an elementary guitar player. I know how to improvise, I know chord progressions, the circle of fourths/fifths, intervals, etc.
I know I7/IV7/V7, I know that I can mix them. But I realized a problem when I saw John Mayer's "Gravity."
This is my question: Why G major and not G7? Why does he use G minor pentatonic?
There are several common ways of approaching a blues or a 'bluesy' song. For a 'sweet' effect you can go hard on the sixth, take it easy on the flat seventh and bend up to the major third. If you want more 'mean/mistreated' you go with the flat seventh, flat fifth and flat third. Or you can mix them up. In this tune John Mayer mixes them up and also rides the major seventh hard at one point. So, the answer to your question is that the blues gives you licence to milk the tension between major and minor, and that goes for the seventh degree as well.
It's the age old thing - while playing over a major/seventh chord sequence, one can and does use both the major and minor pents, it's not a problem. It's the same with maj and min blues - with just an added note in each case. It all works, and good players will be in and out of both in most solos.
